1) Find the Surfaces Tab.
2) Select the Editor Tab.
3) Use the Surface Tool to select the part of your object you want to apply a texture to - that part should then get an orange outline around it.
4) Options will appear for things like Diffuse Color, Specular Color, etc, in the Surfaces Menu. What you want is Diffuse Color.
5) Click the white square next to the Diffuse Color box.
6) A pop-up box will appear - the top option, I believe, is something like 'select file'. That's the one you want.
7) A dialog box will open. Use it to navigate to the file you want.
8) Click Enter, and the selected image should become the texture on the selected part of the object.

If that doesn't work - if you get to the last step and the texture doesn't appear, but the object changes color - the object hasn't been UV mapped. UV mapping is basically unwrapping the 3d object into a 2d plane, letting a texture be applied from a 2d image. There are various programs that let you UV map, but I'm hoping you won't need that because I don't know much about that.